The present invention relates to a process for preparing a block copolymer comprising a polypropylene segment and a poly(ethylene-co-propylene) segment, with the two types of segments being chemically linked. More particularly, the present invention relates to a process for preparing a block copolymer, which process comprises forming a polypropylene segment formed through polymerization and forming a poly(ethylene-co-propylene) segment at an end of the polypropylene segment, in the presence of a catalyst comprising a solid catalyst component, at least one organometallic compound, and, if necessary, an electron-donating compound (e.g., an organosilicon compound and a nitrogenous heterocyclic compound), the solid catalyst component being preliminarily brought into contact with the organometallic compound in accordance with needs.
The thus-produced block copolymer has excellent impact resistance and is useful as a molding raw material, a compatibilizer for a crystalline polyolefin and an amorphous polyolefin, and a modifier for polyolefins such as polypropylene and polyethylene.
Polyolefins such as polypropylene and polyethylene are widely used in consumer goods, due to their excellent properties (e.g., mechanical strength, heat resistance, resistance to chemicals, electrical insulating property), excellent processability, and low cost. Among these polyolefins, polypropylene has comparatively high rigidity but has poor impact strength. In order to improve the impact strength, amorphous poly(ethylene-co-propylene) having high impact strength has been blended with polypropylene. In a conventional block copolymer, a matrix phase comprising polypropylene and a domain phase comprising poly(ethylene-co-propylene) are separated. Therefore, when the block copolymer is subjected to impact, a matrix phase and a domain phase are separated, to thereby generate blushing and degrade physical properties after that. Thus, there is still demand for improving such drawbacks.
Conventionally, a block copolymer comprising polypropylene and poly(ethylene-co-propylene) is known as a type of modified polypropylene. In a conventional process for producing the block copolymer, the polymer is synthesized through a two-step polymerization method; i.e., polypropylene is synthesized in a first polymerizer over 30 minutes to several hours, followed by synthesis of poly(ethylene-co-propylene) in a second polymerizer over 30 minutes to several hours. When the time allotted for forming one polymer chain is taken into consideration, polypropylene and poly(ethylene-co-propylene) contained in the thus-obtained block copolymer are not linked via a chemical bond, and are in a microscopically blended state. Thus, the product is not a genuine block copolymer as defined in polymer chemistry, and satisfactory characteristics commensurate with an object might not be obtained.
Japanese Patent Application Laid-Open (kokai) Nos. 8-92338 and 9-87343 disclose a process for producing a genuine block copolymer in which polypropylene and poly(ethylene-co-propylene) are linked via a chemical bond. In the process, the genuine block copolymer is polymerized within each short time in polypropylene and poly(ethylene-co-propylene)polymerization such that substantially no chain-transfer reaction occurs in the presence of a Ziegler catalyst or a metallocene catalyst by use of a tubular polymerizer.
The above-disclosed genuine block copolymer in which polypropylene and poly(ethylene-co-propylene) are linked via a chemical bond; i.e., polypropylene-b-poly(ethylene-co-propylene), has improved blushing resistance and impact strength, and the above process provides block copolymer material having excellent characteristics.
However, since the polypropylene-b-poly(ethylene-co-propylene) obtained through the disclosed process has a low molecular weight, a higher molecular weight is required in order to improve physical properties, such as mechanical strength, and heat resistance and processability.
In addition, the disclosed process provides polypropylene-b-poly(ethylene-co-propylene) at low yield, and the produced polymer contains a considerable amount of inorganic residues, which causes degradation in quality thereof; e.g., lower processability or generation of fisheyes.
When the disclosed process is carried out at a polymerization pressure of 3 atm or more, the produced polypropylene-b-poly(ethylene-co-propylene) has an n-heptane extraction ratio of more than 20 wt. %. Thus, dissolution of the polymer in a solvent for polymerization, cohesion of the polymer, and adhesion of the polymer to an inner wall of a polymerizer occur, to thereby render control of polymerization temperature difficult. As a result, anomalous polymerization and plugging of the polymerizer might occur. In contrast, when the process is carried out at a polymerization pressure of 3 atm or less, production efficiency decreases.
In view of the foregoing, an object of the present invention is to enhance catalytic activity for producing a genuine block copolymer in which a polypropylene segment and a poly(ethylene-co-propylene) segment are linked via a chemical bond, to thereby reduce the amounts of inorganic residues. Another object of the invention is to provide a genuine block copolymer having a weight average molecular weight of 100,000 or more. Still another object of the invention is to produce a genuine block copolymer exhibiting an n-heptane extraction ratio of 20 wt. % or less without involving adhesion of a polymer to an inner wall of a polymerizer.
The present inventors have conducted earnest studies on a process for producing a genuine block copolymer in which polypropylene and poly(ethylene-co-propylene) are linked via a chemical bond, and have found that ethylene and propylene are copolymerized to an end of a polypropylene segment by use of a solid catalyst component which comprises a solid catalyst component (1) containing titanium and halogen, or titanium, magnesium, and halogen, and which has been preliminary activated by being brought into contact (also referred to as preliminary contact) with a catalyst component (2) containing at least one organometallic compound, within a polymerization period of time in which substantially no chain-transfer reaction occurs, to thereby produce polypropylene-b-poly(ethylene-co-propylene) with high efficiency at high catalytic activity and reduce the amount of residual inorganic matter in the produced block copolymer. The present invention has accomplished on the basis of this finding.
Furthermore, the present inventors also found that the aforementioned drawbacks can be resolved by employing a specific electron-donating compound such as a silicon compound or a nitrogenous heterocyclic compound as an external donor, to thereby attain the present invention.
Accordingly, in a first aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) in the presence of an olefin-polymerizing catalyst comprising a solid catalyst component (1) containing titanium and halogen, or titanium, magnesium, and halogen, and an organometallic compound (2), wherein the solid catalyst component (1) is preliminarily brought into contact with the organometallic compound (2), and then a polypropylene segment is formed through polymerization, followed by formation of a poly(ethylene-co-propylene) segment at an end of the polypropylene segment through polymerization.
In a second aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) in the presence of an olefin-polymerizing catalyst comprising a solid catalyst component (1) containing titanium and halogen, or titanium, magnesium, and halogen; an organometallic compound (2); and at least one electron-donating compound (3) selected from the group consisting of organosilicon compounds represented by RnSi(ORxe2x80x2)4xe2x88x92n (wherein each of R and Rxe2x80x2, which may be identical to or different from each other, represents a C1-C10 hydrocarbon group and n is an integer of 1 to 3) and a nitrogenous heterocyclic compound represented by the following formula (1): 
(wherein R1 represents a C1-C6 hydrocarbon group; each of R2, R3, R4, and R5 represents hydrogen or a C1-C6 hydrocarbon group; at least one of R2 and R3 and at least one of R4 and R5 represent hydrocarbon groups, respectively, and R2 and R3 or R4 and R5 may be linked to form a ring; R6 represents hydrogen or a C1-C6 alkyl group or alkyloxy group; and R7 represents hydrogen or a C1-C6 alkyl group or alkyloxy group), wherein a polypropylene segment is formed through polymerization, followed by formation of a poly(ethylene-co-propylene) segment at an end of the polypropylene segment through polymerization.
In a third aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in the second aspect, wherein the solid catalyst component (1) is preliminarily brought into contact with the organometallic compound (2) in the presence of an electron-donating compound (3).
In a fourth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) in the presence of an olefin-polymerizing catalyst comprising a solid catalyst component (1) containing titanium and halogen, or titanium, magnesium, and halogen, and an organometallic compound (2), wherein a polypropylene segment is formed through polymerization, and then an electron-donating compound as described in the second aspect is added, followed by formation of a poly(ethylene-co-propylene) segment at an end of the polypropylene segment through polymerization.
In a fifth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in the fourth aspect, wherein the solid catalyst component (1) is preliminarily brought into contact with the organometallic compound (2).
In a sixth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in any one of the first to fifth aspects, wherein the organometallic compounds comprise at least two different organometallic compounds represented by RnAlCl3xe2x88x92n (wherein each of R represents a C1-C20 alkyl group, an aryl group, or a C3-C20 cycloalkyl group; and n is an integer of 1 to 3 or a half value thereof).
In a seventh aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in any one of the first to sixth aspects of the invention, wherein a tubular continuous polymerizer including a polymerization zone xe2x80x9caxe2x80x9d and a polymerization zone b located downstream of the zone xe2x80x9caxe2x80x9d is used and a polypropylene segment is formed through polymerization in the polymerization zone xe2x80x9ca,xe2x80x9d followed by formation of a poly(ethylene-co-propylene) segment at an end of the polypropylene segment through polymerization in the polymerization zone xe2x80x9cb.xe2x80x9d
In an eighth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in the seventh aspect, wherein each of residence times in the polymerization zone xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d is 0.01 second to 15 minutes.
In a ninth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in the seventh aspect, wherein reaction in the tubular continuous polymerizer is carried out in a plug-flow manner.
In a tenth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in any one of the first to ninth aspects, wherein a weight average molecular weight is 100,000 or more.
In an eleventh aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in any one of the first to ninth aspects, wherein an n-heptane extraction ratio is 20 wt. % or less.
In a twelfth aspect of the present invention, there is provided a process for producing polypropylene-b-poly(ethylene-co-propylene) as described in any one of the first to ninth aspects, wherein the amount of inorganic matter derived from a catalyst is 100 ppm or less.